What are flaky and elongated aggregates? How can the shape of aggregate influence strength of concrete? Following is the result of a sieve analysis of 500 gm aggregate:
| IS sieve size | 10 mm | 4.75 mm | 2·36 mm | 1·18 mm | 600 micron | 300 micron | 150 micron | lower than 150 micron |
| Weight retained in gm | 0 | 10 | 50 | 50 | 95 | 175 | 85 | 35 |
Find out the 'Fineness Modulus' of the sample
FLAKY AGGREGATES:- This agg. Are those whose least dimension i.e. thickness is less than 3/5 th of their mean dimension.
ELONGATED AGGREGATES:- This agg. are those whose greater dimension i.e. length is greater than 9/5 th of their mean dimension.
According to shape voids
Rounded aggregate 32 – 33 %
Irregular aggregate 35 – 38 %
Angular aggregate 38 – 40 %
Rounded aggregate gives better workability and Angular aggregate gives better strength.
total wt. = 500gm.
| Sieve | Wt. retained in each sieve(gm) | % wt. retained | cumulative % of wt. retained | % finer |
| 10 mm | 0 | 0 | 0 | 100 |
| 4.75 mm | 10 | 2 | 2 | 98 |
| 2.36 mm | 50 | 10 | 12 | 88 |
| 1.18 mm | 50 | 10 | 22 | 78 |
| 600 µ | 95 | 19 | 41 | 59 |
| 300 µ | 175 | 35 | 76 | 24 |
| 150 µ | 85 | 17 | 93 | 07 |
| <150 µ | 35 | 7 | 100 | 00 |
| Ƹ = 346 |
So, F.M. = 346/100 = 3.46
F.M. of coarse aggregate is3.46.
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